Crowdin - Localize your product in a seamless way
Gorm - Gorm .po file editor
POEditor - The translation and localization management platform that's easy to use *and* affordable!
Weblate - Weblate is a free web-based translation management system.
Better PO Editor - Better PO Editor is an editor for .po files, used to generate compiled gettext .
Translate Toolkit - The Translate Toolkit is a localization and translation toolkit.